The present application will pursue the following objectives: (1) Prolongation of allograft survival after in vitro culture. a) To determine the optimal (least toxic to other cells) tissue culture conditions which will kill donor leukocytes (macrophages); b) To determine if these conditions will allow survival of thyroid and pancreatic tissues in tissue culture as evidenced by histological examination; c) To determine if these conditions will allow survival of thyroid and pancreatic tissues in tissue culture as evidenced by functional tissue; d) To determine if the successful "optimal conditions" found in part 2 will permit successful allogeneic thyroid and pancreas transplantation first, in the mouse, and later in a larger animal, the Yucatan Miniature Pig. (2) The induction of Arginase in macrophages. a) Purification of mouse liver and peritoneal cell arginase and production of antisera to these proteins; b) Determine the specific cell type in the peritoneal cell population producing the arginase and determine whether the increase in arginase represents increased synthesis, decreased secretion or an unmasking of an inactive precursor; c) Examine the role of prostaglandins and cyclic nucleotides in arginase production; d) Isolate and identify the tumor cell product which contributes to the increases of arginase; e) Determine if a correlation exists between a tumor's ability to cause an increase in macrophage arginase and its ability to produce immunosuppression.